hso: Fix for 5 sec timeouts with v2.x firmware

Don't send flow control settings to any port other than the modem port.
Older firmware ignored this request but did sent a reply. Newer firmware just
ignores it without reply and causes a 5 second timeout every time a port
(except for the modem port) is opened or if tiocm settings are changed.
Signed-off-by: NJan Dumon <j.dumon@option.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/usb/hso.c

@@ -1723,6 +1723,10 @@ static int hso_serial_tiocmset(struct tty_struct *tty, struct file *file,
 		D1("no tty structures");
 		return -EINVAL;
 	}
+
+	if ((serial->parent->port_spec & HSO_PORT_MASK) != HSO_PORT_MODEM)
+		return -EINVAL;
+
 	if_num = serial->parent->interface->altsetting->desc.bInterfaceNumber;
 
 	spin_lock_irqsave(&serial->serial_lock, flags);